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DOS汇编源码系列教程——cldoc12

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这个都是过去DOS时代的汇编源码,虽然已经过去了,但是对于学习汇编还是有帮助的,汇编语言只是程序员一门基础语言,大多人掌握即可,不一定要深入研究.......
;************************************************************************
;*                                   *
;*   CleanDoc 1.2 (C) 1997 RonSoft.                 *
;*                                   *
;*   This is a simple litte assembler program that cleans out    *
;*   the documents folder in the start menu.             *
;*   This is version 1.2                       *
;*   There's no command line switches and stuff.           *
;*   It gives NO messages if everything goes allright.        *
;*   It check for a environment variable called CLEANDIR and CD:s  *
;*   down to that dir if the variable is found. If not it uses    *
;*   the default WINDOWSRECENT directory and deletes(UNLINKS)    *
;*   EVERYTHING it finds there, and CD:s back to where it started  *
;*   from.                              *
;*                                   *
;*   Comments, suggestions:                     *
;*   Ronald Nordberg.                        *
;*   Silverven 3                          *
;*   907 50 Ume?                          *
;*   Sweden.                             *
;*   http://home2.swipnet.se/~w-20064                *
;*   christine.martinson@swipnet.se                 *
;*                                   *
;*   THIS PROGRAM ARE COPYRIGHTED FREEWARE.             *                                   *
;*                                   *
;************************************************************************
                    ;some euqates for readability
kbd       equ   16h       ;keyboard irq
msdos      equ   21h       ;MSDOS irq
reset      equ   0dh       ;disk reset
dfopen     equ   0fh       ;open disk file
dfclose     equ   10h       ;close disk file
searchf     equ   11h       ;search first
searchn     equ   12h       ;search next
seqread     equ   14h       ;sequential disk read
seqwrite    equ   15h       ;   "    " write
getdisk     equ   19h       ;get current disk(default)
setdta     equ   1ah       ;set disk transfer area address
setdir     equ   3bh       ;set current directory
createf     equ   3ch       ;create file with handle
openf      equ   3dh       ;open file with handle
closef     equ   3eh       ;close file with handle
readf      equ   3fh       ;read from file with handle
writef     equ   40h       ;write to file with handle
unlink     equ   41h       ;UNLINK(delete file)
getdir     equ   47h       ;get current directory
allocmem    equ   48h       ;allocate memory
freemem     equ   49h       ;free memory
changebs    equ   4ah       ;change block size
findfirst    equ   4eh       ;find first file
findnext    equ   4fh       ;find next file
exit      equ   4c00h      ;msdos exit
envir      equ   2ch       ;offset ENVIRONMENT block
[BITS 16]                ;NASM STUFF !?
[ORG 100h]
    mov   ax,cs          ;get code segment
    mov   ds,ax          ;use it now
    mov   [comseg],ds
    mov   [extseg],es
;************************ setup and preparing ***************************
main:
    mov   ah,setdta        ;set our DTA-area
    mov   dx,mydta        ;buffer for it
    int   msdos          ;call dos
    mov   ah,getdisk       ;get default drive
    int   msdos          ;call dos
    add   al,41h         ;drive in al, make it ASCII
    mov   byte [curdir],al    ;fill buffer with name (A:..etc)
    mov   byte [path],al     ;and default path
    mov   word [curdir+1],":"  ;copy separator to path
    mov   si,curdir        ;pointer path buffer
    add   si,3          ;offset doscall part
    mov   ah,getdir        ;get current dir
    mov   dl,0          ;0 = default
    int   msdos          ;call dos
    jnc   diskok         ;ok
    mov   bx,errt0        ;could not find current dir ?? If You
    jmp   errout         ;get an error here You probably have
diskok:                 ;forgot to turn on Your computer.
    call  getenv         ;check out if any ENV var
    cmp   dx,-1          ;was it there
    je   findfile        ;yeahh
    mov   dx,path         ;noo way, use default path
    mov   ah,setdir        ;cd down
    int   msdos          ;call dos
    jnc   findfile        ;all ok
    mov   bx,errt1        ;error
    jmp   errout         ;skip
;*************************** the delete file loop ***********************
findfile:
    mov   ah,findfirst      ;see if the files out there
    mov   cx,0fh         ;all files
    mov   dx,files        ;our NULL terminated filname(*.*)
    int   msdos          ;do the stuff
    jnc   delit          ;all ok, must delete first file
    jmp   goback         ;error, CD back and skip
found:                 ;found something
    mov   dx,files        ;files (*.*)
    mov   ah,findnext       ;the function
    int   msdos          ;call dos
    jc   goback         ;no more files, quit
delit:
    mov   ah,unlink        ;UNLINK (delete) file
    mov   dx,mydta        ;pointer Disk Transfer Area
    add   dx,30          ;offset Filename
    int   msdos          ;delete it
    jnc   found          ;deleted ok
    mov   bx,errt2        ;could not delete it ????
    call  write          ;let us know
    mov   bx,mydta        ;show wich file
    add   bx,30          ;offset filename in DTA
    call  write          ;write out filename
    mov   bx,linefeed       ;linefeed
    jmp   errout         ;and skip
goback:
    mov   ah,setdir        ;CD back to origin
    mov   dx,curdir        ;path to dir
    int   msdos          ;do it
    jnc   quit          ;all ok, proceed
    mov   bx,errt1        ;error, get text
    ;*************************** errorexit ***********************
errout: call  write          ;show errormessage
quit:
    xor   eax,eax         ;clean out that
    mov   ax,exit         ;MS-DOS successful exit
    int   msdos          ;back to the operating system
;***************** get ENVIRONMENT var if any *****************
getenv:
    push  es           ;now check if there's any
    push  ds           ;environment variable
    mov   es,[es:+2Ch]      ;ES:DI points at environment
    xor   di,di          ;which is paragraph-aligned
floop:
    cmp   byte [es:di],0     ;if we got 2 zeroes in a row
    jne   goon          ;we are at the end of the ENV
    cmp   byte [es:di+1],0    ;variables
    je   eout
goon:             
equal: cmp   byte [es:di],'C'    ;is it our variable ?
    jne   flop
    inc   byte di
    cmp   byte [es:di],'L'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'E'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'A'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'N'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'D'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'I'
    jne   flop
    inc   byte di
    cmp   byte [es:di],'R'
    jne   flop
sign:  inc   byte di         ;dump the R
    inc   byte di         ;dump the =
    mov   ax,es          ;make DS:DX point to string we found
    mov   ds,ax
    mov   si,di
    mov   bx,si
    mov   dx,bx          
    mov   ah,setdir        ;func Set Current Directory(CD)
    int   msdos          ;do it
    jnc   envok          ;all ok, proceed
    mov   dx,0          ;clear flag (use default dir)
    jmp   eout          ;return
flop:  inc   byte di         ;next byte
    cmp   byte [es:di],0     ;a 0 ?
    jne   flop          ;noo
    inc   byte di         ;yeahh, dump it
    jmp   floop          ;check if two
envok: mov   dx,-1
eout:  pop   ds
    pop   es
    ret
;*************************************************************************
;*    Writes out the NULL terminated text supplied in BX.       *
;*    OR writes out data,BX and size,CX if called at lwrite.     *
;*************************************************************************
write: pusha
    mov   si,bx          ;copy to SI
    mov   cx,0          ;clear count
wloop: lodsb              ;load AL with SI
    cmp   al,0          ;end of line ?
    je   lwrite          ;yeahh
    inc   cx           ;no, incrase byte count
    jmp   wloop          ;test next byte
lwrite: mov   dx,bx          ;text address in DX
    mov   bx,1          ;filehandle standard output = 1
    mov   ah,writef        ;MS-DOS writefile with handle is 040
    int   msdos          ;write buffer to standard output
    popa
    ret               ;done
;************************ DATA and BSS stuff ***************************
comseg:     dw   0
extseg:     dw   0
utext:     db   "CleanDoc V1.2 (C) 1997 RonSoft",13,10,0
errt0:     db   "Could not find current directory !",13,10,0
errt1:     db   "Directory not found.",13,10,0
errt2:     db   "Could not delete ",0
path:      db   " :WINDOWSRECENT",0 ;default path without DRIVE
files:     db   "*.*",0
linefeed:    db   13,10,0
mydta      times 128 db 0  ;use 128 bytes as DTA   NASM stuff !
curdir     times 68 db 0  ;use 64 + 4 bytes for current dir
    END  
 

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